Use of a highly focused laser beam for optical recording permits the storage of very large quantities of information at extremely high data rates and also allows for rapid random access to segments of the data during playback of information. Applications of this technique are many and the background art has taught optical information storage media wherein the recording process comprises thermal deformation of a homogeneous layer, involving physical and/or chemical means such as pits, recessed areas, and hole forming, bubble and protuberance forming, ablating, subliming, melting, fusing, softening, coloring or discoloring, and the like. Many of these processes are described in "Proceedings of the Symposium on Optical Storage Materials," in the Journal of Vacuum Science & Technology, Vol. 18(1), Jan/Feb (1981) 63-110. "CRC Critical Reviews", Solid State and Material Sciences, Volume 13, Issue 1, (1986) pages 1-26 reports four laser writing modes, deep pit, shallow pit, bubble formation and optical property change. While the first three modes are destructive, the last involves some optically detectable chemical or physical change in the recording medium without topological disruption of the layer. This article states that "although several examples of such recording media exist among the inorganics,--there are no reported cases of all-organic media that function by this mechanism." Critical Reviews, p.12-13. These and other state-of-the-art means, including ablating, detexturing, phase changing, alloying, particle coalescing, vesicular or bubble forming, have also been described by M.D. Croucher and M.A. Hopper, "Materials for Optical Discs," in Chemtech, July, 426-433 (1987).
U.S. Pat. Nos. 4,725,525, 4,556,893, 4,551,828, 4,551,413, 4,241,355, 4,492,750, 4,298,975, 4,219,826, and 4,218,689 teach thermally deforming products and processes.
An article, "Erasable Optical Discs" in Popular Science, May, 1987, pp. 56-59, and 101-102, illustrates phase-change recording, wherein a typical tellurium-based layer can be continuously switched from a crystalline to a noncrystalline or amorphous state by heating with a proper laser.
U.S. Pat. No. 4,422,159 teaches an optical recording structure which includes connected and disconnected voids which upon laser exposure melt to alter the optical properties of the treated region.
In all the prior art patents, it is either stated explicitly or shown implicitly in the drawings that any or all of the recording layers are uniformly homogeneous and isotropic in their material properties before the recording process, but after the recording process are anisotropic and inhomogeneous along the direction perpendicular to the layer plane by virtue of ablation and/or deformation occurring upon exposure to the laser beam.